A problem which occurs in some applications of coated woven fabric is loss of adhesion between the coating and the woven layer due to water. This problem occurs not so much in applications like vehicle tyres as in applications where the coated fabric is to be in considerable contact with water and where there may be access for water to an exposed area of the coated fabric. One particular application in which this problem occurs is in the skirts of gas cushion vehicles which are to travel over water. At least in the United Kingdom gas cushion vehicles which are self-propelled are popularly known as "hovercraft" and this term will be used, for convenience, in the remainder of this specification.
The skirt system of a hovercraft consists basically of a loop or of a bag to which are attached segments or fingers (hereinafter referred to as "fingers") which actually contact the ground or water over which the hovercraft travels. The fingers deteriorate more rapidly than the loop or bag. In the case of hovercraft which travel over land most of the deterioration is due to abrasive wear resulting from contact with the ground. For hovercraft which travel wholly or mainly over water the reasons for deterioration are more complex. Wear can take place due to contact with water and to mutual contact and rubbing between areas of the finger. However a failure typical of hovercraft travelling over water is associated with the breakdown of adhesion between the rubber and fabric in the lower parts of the fingers. This is due to the very severe flexing to which the material is subjected.
The coated material which is used for the manufacture of the skirt system components is generally composed of a base fabric of nylon treated with an adhesive and then coated with a natural or synthetic rubber compound. The adhesive is generally a resorcinol-formaldehyde-polymer composition deposited from an aqueous mixture of resorcinol, formaldehyde and a type or types of polymer latex compatible with the natural or synthetic rubber compound which is afterwards applied. Alternatively a solvent-based cement of a polymer composition into which an organic polyisocyanate solution is stirred may be used for treating the fabric and in this case the dried adhesive film consists of an intimate mixture of the polymer and a polyisocyanate. After coating the natural or synthetic rubber compound is vulcanised or cross linked by methods well known in the polymer industry, unless it is thermoplastic when it would be subjected to a heat treatment.
The breakdown in the adhesion between the natural or synthetic rubber compound and fabric in the case of hovercraft travelling over water is due to the flexing to which the material is subjected, as has already been stated. However the breakdown is accelerated by the weakening of the adhesive due to the diffusion or permeation of water into the adhesive layer.